Wireless communications systems typically provide interconnect and/or dispatch voice communication services. Interconnect voice communication services are those typically provided by most wireless carriers as circuit-switched communications. Dispatch communication services are commonly known as walkie-talkie or push-to-talk (PTT) types of calls, such as the Nextel Communications, Inc. service identified by the trade name Direct Connect. Interconnect voice communication services provided by most wireless carriers can be provided between sources and destinations of different wireless carriers.
A device that has telephony features with dispatch functionality requires a state machine to determine what the next valid action is in response to various inputs, either from the user, from the device's operating system (OS) or from a carrier network. Examples of the device include: a mobile phone and a handheld computer with dispatch functionality, such as a personal digital assistant (PDA) or a Pocket PC (PPC) with a mobile phone application program. An operating system is the basic platform that the device runs on. The purpose of an operating system is to organize and control hardware and software so that the device it resides in behaves in a flexible but predictable way. An example of an operating system used for PPCs is Microsoft's Windows Mobile 2003 for Pocket PC (MS 2003 PPC OS). The MS PPC 2003 OS enhances the ability to communicate and to send, receive and manage data while mobile.
Wireless technologies, such as CDMA and GSM devices, include a Radio Interface Layer (RIL) for the MS PPC 2003 OS. The RIL is an interface layer between the OS and an RF module in the PPC. However, the RILs of the CDMA and GSM devices do not incorporate the added functionality of dispatch calling and their state machine is simpler.